Hi,
This is from a guy. Tell him your concerns. It may be difficult, but tell him. And if he is a normal guy, telling him that since he is so "big"you are afraid it will hurt will make him feel really proud of his equipment. We men a such suckers!
But tell him your concerns. If possible, hold hands while you do it. somehow that makes things easier.
Do not owrry about your body. I agree with advice given above. I have seen a reasonable number of naked female bodies from very close up

. All sizes and shapes. Each had its own special features. We guys are not looking for imperfections, we just view the overall package. And one of the most important parts of that package is how you feel about yourself. Be relaxed, be what you are - you.
If he does not "like" to see you naked becuase you are too "something" then he is probably a lost cause. Don't worry.
Try to relax. Tell him you are having trouble relaxing. communicate. Tell him how you feel. Tell him if you are embarassed for him to see you naked, or whatever. Work with him to slowly, step by step, overcome this issues.
communicate, communicate, communicate. Tell him how you feel, even if you know in your head that the way you feel is not really logical. Tell him that - "I know this is not logical but I feel xxxxxxx." He cannot read your mind, and you cannot read his.
Godd luck.